The gloves came off early when Nelson, the Democratic nominee, attacked McCollum, a member of Congress for 20 years, for voting against measures to limit the sale of guns at gun shows and a three-day waiting period for buying guns.

Then he accused the Republican of voting to cut Medicare funding -- a charge McCollum forcefully denied.

"I have never, ever voted to cut Medicare," McCollum said. "I have always voted for dramatic increases. So, what you said was a lie. It's not true. I challenge you on that."

Nelson quickly came back to the issue, saying, "I'm not going to let my opponent run and hide from his record."

The Democrat cited a 1995 vote on the federal budget that included what he described as a "cut of $270 billion in the Medicare trust fund."

Serving as the first time most voters will be able to judge the candidates in a format longer than their 30-second attack ads, the debate -- to be broadcast Sunday evening -- produced no major gaffes by the candidates. It focused mainly on issues that have already surfaced in campaign stump speeches and commercials.

McCollum fought back by repeatedly trying to tie Nelson, the state's insurance commissioner, to increases in insurance rates. He accused his main opponent of failing to encourage more competition in the insurance market.

"You can't hide from the facts," McCollum said, turning to face Nelson. "The facts is the facts. Insurance rates have gone up 70 percent in your tenure. The truth is, we have fewer choices."

Then, in one of the more heated portions of the debate, Nelson said "McCollum's friends" -- meaning GOP state legislators -- were responsible for creating arbitration panels in 1996 that took away the insurance commissioner's rate-setting powers.

Both candidates said they want to eliminate the arbitration panels.

Nelson said McCollum had filed legislation in Congress that would jack the rates of insurance for homeowners extremely high. The move "was well-intentioned but would have caused humongous rate increases," he said. He was referring to a measure expanding a catastrophic insurance fund. McCollum aides said after the debate that Nelson had previously supported it.

The major-party candidates almost ignored Logan, an independent candidate and Democratic state representative from Opa-locka who used his debate appearance to decry his rivals' tax-cut proposals as ones that will primarily benefit the wealthy.

On several occasions, Logan shook his head in amusement at McCollum and Nelson's needling of one another.

"There are stark differences between us, one of which is they all like me and don't like each other," Logan said, drawing laughter in one of the few lighthearted moments of the debate.

The high-stakes debate came against a backdrop of ads and accusations about voting records, attendance in Congress and philosophies of governance.

The two-hour forum, Web-cast live on the Internet and taped for broadcast Sunday on most PBS stations. The three candidates stared at the cameras and rarely looked at one another while they stood only a few feet away on a debate stage at the Crest Theatre in Delray Beach. It was the first of three televised debates in which McCollum and Nelson hope to make an impression before large audiences in the final weeks of the campaign.

The remaining debates will be held in Tampa and Orlando, and will be carried live by broadcast networks.

After the first hour of a conventional debate format, audience members and Internet users questioned the candidates on issues ranging from gay marriages to Social Security benefits. But the responses were generally terse and rehearsed. That second hour will not be televised.

Up to now, the Senate race has been overshadowed by the presidential campaign, which has been unexpectedly competitive in Florida. Recent polls have found Nelson enjoying a modest lead over McCollum, with Logan a distant third, drawing support from between 3 and 6 percent of those surveyed.

The debates are viewed as a potential turning point in the race, coming as many Floridians begin to familiarize themselves with the candidates.

The outcome of the election will determine whether Democrats can reclaim a seat they lost in 1988, when Republican Connie Mack replaced Lawton Chiles. Since then, Republicans have largely taken control of state and federal elective offices.

McCollum, who compares himself to Mack, has said he hopes the debates will jump-start his campaign in the same way Mack bounced ahead after a strong debate performance in 1988.

Logan, who has complained that his campaign has been largely ignored by the state's major news organizations, also hopes the debates give significant statewide attention to his self-described "maverick" candidacy.